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jedl of much intercfl both to the geologift and tlie chemica! 

 philofopher. The fimilarity of its effefts with thofe of 

 oxygen and acids, have been pointed out in a very ftriking 

 manner by Mr. Hume in the paper before referred to. 



There is a remarkable fimihtude in the effefts of oxygen 

 and filex on the metals, particularly in that procefs called 

 vitrification, which is, in every meaning of the word, a 

 complete faturation and oxydation. By mc-ans of filex, all 

 the metals (perhaps without exception), from being the 

 moil opaque bodies in the univerfe, may be rendered quite 

 pellucid, affordinfj an endlefs variety of the moft charming 

 tints. It is chiefly from metallic fubftances that the moft 

 durable colours are obtained, particularly for tlaining glafs, 

 and making artificial gems. The bell opaque colours, 

 fuch as are molt fuitable for enamel, water, oil, crayon, and 

 all other defcriptions of painting, are derived alfo from the 

 metals combined either with filex or oxygen. Even the 

 precious ftones, and the lefs valuable cryllals and pebbles, 

 with an infinite number of mineral produdlion'', feem to 

 derive their beauty and value from the aftion of filex on 

 the metals. Thus, the opacity of lead is effedlually changed 

 by the fand or filex ufed in the compofition of flint-glafs, 

 and the compound is rendered not lefs diaphanous, than 

 when, by means of oxygen, the fame metal is diflblved in 

 dilute nitric acids. 



The power which filex exercifes over potafh and foda, 

 and a variety of other fubftances which enter into the com- 

 pofition of glafs, is a ftriking and well-known inftance (fays 

 Mr. Hume) of its neutralizing efficacy ; for no acid more 

 completely obtunds the acrimony of alkaline bodies, and 

 difarms them of their corrofive charadler. The eff'ervefcence 

 which refults when filex and the alkali enter into fufion and 

 form this taftclefs compound, is net obfervable till the mate- 

 rials are on the point of perfeft combination ; hence, as 

 fomething is apparently evolved, neither oxygen nor any 

 other aeriform fluid can be fuppofed to enter ; fo that the 

 acidifying power (if the term may be applied) which appears 

 to coerce the alkaline matter, is alone due to the fand 

 which is ufually employed to form glafs. Indeed vitrifica- 

 tion feems, in all inllances, to be accomplilhed by filex, or 

 by oxygen, and the glafs of lead, of antimony, of phof- 

 phorus, borax, or any other body, is due to the one, as 

 much as the glafs in common ufe is to the other of thefe 

 oxygenating agents. 



The power of filex, as an oxydizing, faturating, and 

 neutralizing agent, is by no means confined to rocks, 

 minerals, and the inanimate parts of created matter ; but it 

 pervades alio, as an efiential element, the ftrufture of 

 organized beings, and occupies a diftingniflied place both 

 in the animal and vegetable economy. " Nothing is more 

 aftonilhing," fays Dr. Smith, " than the fecretion of flinty 

 earth by plants, a faft which is well afccrtaincd." Ac- 

 cording to modern experiments, human hair, and probably 

 the hair of all animals whatever, alfo contains filex as a 

 conftituent clement. 



From numberlefs phenomena that admit of no other in- 

 terpretation, it may juftly be inferred, fays Mr. Hume, 

 that nature polftlles means of converting filex into other 

 forms, and of fo interweaving it into the conftitiition of her 

 varied works, that it ceafes entirely to appear Ih its original 

 flate. Every thing conneftcd with the progrcfs of animal 

 and vegetable cxillence, witli the infcnitahle fecrets of the 

 aflimilating powers, or with the phyfiology of all organized 

 matter, fhevvs that tranfmutation is an operation which we 

 cannot difprove, though we may not be able to trace it 

 through all its llcps. 



According 19 Bcrzelius, filex, or filica, confidcred aa an 



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acid, pofteffes the property of giving filiciates of many dif- 

 ferent degrees of faturation. The moft general is that in 

 which filex contains the fame quantity of oxygen as the 

 bafe : thefe he denominates (imply Jl/iciatei. The next moft 

 general are thofe in which filex contains three times theoxygeu 

 of the bafe ; thefe he calls trijiliciales : it not unfrequently 

 contains twice the oxygen of the bafe ; thefe combination* 

 he calls hifdiciata. Silex alfo produces a great number of 

 combinations with exccfs of bafe of difi'erent degrees, which 

 he denominates fubfilictales , to which again he applies the 

 appellations li, tri ; for example, bialummous fubftlielaU, tri- 

 aluminous, l^c. all announcing that the bafe contains twice 

 or three times the oxygen of the filex. 



Silex, like other acids, gives alfo double filiciates, partly 

 with and partly without water of cryftallization. We moft 

 frequently find, that the bafes which have a tendency to 

 produce double falls with other acids, do the fame thing 

 here : in the fame manner, as in the double filiciates, we 

 again find (although with many exceptions) the fame pro- 

 portion between the bafes as in the other previoudv known 

 falts with double bafes. Hence, for example, if in com- 

 mon felfpar we could exchange filex for fulphur, the com- 

 bination would be alum without water. 



But Nature in her rich ftores, fays Berzelius, exhibits 2 

 number of combinations of filex ftill more various, for which 

 we have few if any analogous combinations to produce from 

 the experiments in our laboratories. Thus we find filiciatei 

 with from three to four bafes, which all form one common 

 combination, whofe pure cryllalline ftrutture feems to render 

 it evident that it mull be confidcred as one chemical whole ; 

 unlefs it fliould hereafter be proved that fuch bodies belong 

 to the clafs of cryilals that are formed of many different 

 fubftances lying in juxtapofition, but not chemically com- 

 bined. 



It often happens, alfo, that thefe numerous filiciates are 

 not of the fame degree of faturation, but that one or more 

 of the weaker bafes are fubfihciates, or filiciates, while one 

 or more of the ftronger are bi or /ri-filiciates. That fimilar 

 combinations are not formed in our laboratories, arifes evi- 

 dently from the rapid and violent means by which thefe 

 combinations are eftedled, which will not admit the a^lioii 

 or influence of thofe weaker affinities which take place in 

 the fecret and undilturbcd rcceffcs of the mineral kingdom. 

 As it is of importance to afccrtain the quantity of oxygen 

 in filex, in order to determine its proportions in the different 

 combinations of filiciates, Berzelius, from various expe- 

 riments made by himfelf and others, eftimates the propor* 

 tion of oxygen to be 49.64. See Silex. 



SILICULA, in Botany, the diminutive of SiLlQUA, 

 (fee that article,) is a Pouch, or pod of a (hort, or rounded, 

 figure, along both the edges of whofe partition the fcedt 

 are inferted ; witncfs the Draba verna, or Whitlow-grafs, 

 fo common on walls in the fpring, and the Thiafpi Burfa- 

 paflorii. Shepherd's purfe. The partition is always really 

 parallel to the valves, though the latter are often fo pro- 

 tuberant, as in the Thiafpi, that their depth is much greater 

 tlian the real diameter of the fruit. Hence Linnxus ha* 

 fallen into an error, firll deteftcd by Mr. Brown, in the 

 charaftcr of SuBUL.MilA. Sec that article. 



SILICULOSA, the firft of the two orders of the lyth 

 clals in the I.,inn;ean fyftem, Tetuadynamia, (fee that 

 article,) the charaftcr of which order coiifills in the (hort, 

 or rounded, not oblong, form of the feed-vcllel. Sec Sl- 

 LICUI.A. 



SILIFREY, in Geography, a town of Africa, in the 

 kingdom of Barra. 

 SILILICON, ID Botany, a uame given by fome of the 



old 



